1. Field of the Invention
The present invention relates generally to satellite communication systems and, more particularly, to such a system which communicates from a communication hub to a remote station on one band and from the remote station to the hub on another band.
2. Description of the Related Art
Modern telecommunication systems provide means for communicating vocal conversations, email, and various kinds of data from originating sources to destinations over twisted pair landlines, coaxial cables, fiber optic cables, and radio frequency communication links. Satellite communications have become an important mode of communications for large and small entities for both one-way services, such as television signals, and two-way services such as data processing services, satellite internet services, and the like. Two-way communication satellite services are typically set up as a head-end or hub station which is interfaced to a large scale communication network, such as the public switched telephone network (PSTN) infrastructure, and remote stations which communicate through a communication satellite to the hub station and through the hub station to the PSTN. The PSTN provides conventional telephone services and data communication over dedicated lines, the internet, and other links. Equipment for remote satellite stations has evolved to what is known as VSAT or very small aperture terminal satellite dishes.
The present standard for VSAT satellite communications is the use of Ku band (12 to 18 GHz) satellite technology in order to use meter or sub-meter sized satellite antennas and to avoid costly licensing and frequency coordination. The problem with Ku band satellite technology is that it is highly susceptible to local rain or weather fade due to the nature of the frequencies used. For this reason, networks have to be tolerant of frequent signal fades or outages during the presence of rain, snow, and storm clouds. This occurs in all Ku band transmissions whether it is for residential satellite television or VSATs.
Some networks attempt to mitigate the fade through the use of automatic uplink power control at the customer VSAT location. This technology gradually increases the transmit power at the remote customer location via a command from the hub location when the hub location senses that there is attenuation somewhere in the path between the remote location and the hub. This works some of the time quite well, but the same local weather anomaly that causes the problem with the inbound signal to the hub also creates a problem with the outbound power control signal to the remote site. Eventually, the control signal cannot reach the remote site electronics with sufficient strength and the remote site shuts down until it can receive a valid command.
This is very bad for reliability and, as a result, Ku band networks are generally designed to be out of service for about 50 hours per year due to weather. For government and customer applications that need to know weather and other critical information, these 50 hours of down time cannot be tolerated.
Heretofore there has not been available a dual-band satellite communications system with the features and elements of the present invention.